Assassin's Creed 2, where can I find Leonardo da Vinci in Sequence 14?

I've been to his workshop but you can't get in there. Thought it would have a bug then on the card everything removed and turned on again. Restarted game + console (Xbox 360). Can't help anyone else?

A possible explanation offers the page:

https://www.4players.de/4players.php/walkthrough/Cheats/14848/75708/Assassins_Creed_2.html

when it comes to the DNA sequence Veni, Vidi, Vici.

(a long time ago that I played the game)

One is displayed